What We Are Trying to Find

byPaul GilsteronFebruary 28, 2018

What is it we are looking for when we probe nearby planetary systems? Certainly the search for life elsewhere compels us to find planets like our own around stars much like the Sun. But surely our goal isn’t restricted to finding duplicate Earths, if indeed they exist. A larger goal would be to find life on planets unlike the Earth — perhaps around stars much different from the Sun — which would give us some idea how common living systems are in the galaxy.

And beyond that? The ultimate goal is simply to find out what is out there. That takes in outcomes as different as widespread microbial life, perhaps leading to more complex forms, and barren worlds in which life never emerged. A galaxy filled with life vs. a galaxy in which life is rare offers us two striking outcomes. We ignore preconceptions to find out which is true.

Flaring Red Stars

Let’s try to put Proxima Centauri’s recent flare, discussed yesterday, in context. Events like this highlight our doubts about the viability of red dwarf systems in developing life. Flares are not uncommon on ultra-cool dwarf stars, meaning nearby planets in any habitable zone (as defined by liquid water at the surface) would be bathed in ultraviolet and X-rays. We face the distinct possibility that such planets might have never become habitable in the first place, their oceans vaporized, their atmospheres hopelessly compromised.

I’m interested to see how Amaury Triaud and Michaël Gillon see things. It was their team at the University of Liège in Belgium and the University of Cambridge that did the initial work on TRAPPIST-1, a red dwarf around which ultimately seven planets were found to orbit. As the scientists point out in a recent essay for Big Think, three of the planets here are intriguing from the standpoint of habitability, and we’ve recently seen new work on their potential atmospheres.

This is what is so exciting about red dwarfs. While we continue to look for rocky worlds around G-class stars, we’re putting the tools for studying red dwarf planets to use right now. Consider what we’ve learned already: TRAPPIST-1 d, e and f do not show signs of puffy atmospheres rich in hydrogen, which goes a long way toward eliminating them as Neptune-like worlds, and leaves open the issue of more compact atmospheres that could sustain life. We’ve also had a fine-tuning of mass estimates (see TRAPPIST-1: Planets Likely Rich in Volatiles). Thus a star producing a scant 0.05 percent as much light as the Sun is beginning to yield its secrets.

Triaud and Gillon look at the path forward, pointing to atmospheric work with the James Webb Space Telescope. It’s clear they have little patience with those content to rule out habitability without a great deal of further evidence. The arguments they examine are familiar: Planets around such stars may be tidally locked, and indeed, in systems like TRAPPIST-1, so tightly packed that they would produce major instabilities. They acknowledge the flare problem Proxima Centauri has so vividly demonstrated.

But what we are dealing with is a set of unknowns, and the exciting thing is that we are closing in on the ability to produce answers to many of these objections. From the essay:

Far from holding us back, those arguments motivated us. Now we can assess the actual conditions, and explore counter-arguments that Earth-sized planets around stars such as TRAPPIST-1 might in fact be hospitable to life. Oceans and thick atmospheres could mitigate the temperature contrast between day and night sides. Tidal interaction between close-orbiting planets might provide energy for biology. Some models suggest that planets forming around ultra-cool dwarfs start out with much more water than Earth has. Ultraviolet radiation could help to produce biologically relevant compounds… We are optimistic.

It’s the nature of that optimism that we need to explore. For Triaud and Gillon are not overlooking the problems of astrobiology here to insist on a result they want to see. Instead, they’re pointing to a demonstrable fact: In our rush to find a ‘twin’ of the Earth, we sometimes forget that our planet is not necessarily the template for life elsewhere. Indeed, searching for an Earth twin is a highly conservative approach. “Research should be about finding what we don’t already know,” they argue, and in the case of exoplanets, that certainly encompasses the nature of the 75 percent of the galaxy comprised of red dwarfs down to tiny ultra-cool stars.

Image: This artist’s impression shows two Earth-sized worlds passing in front of their parent red dwarf star, which is much smaller and cooler than our Sun. Astronomers using the Hubble instrument recently used transmission spectroscopy, in which starlight passes through potential atmospheres of planets, to look for evidence of extended hydrogen atmospheres around several TRAPPIST-1 planets. The lack of such atmospheres makes it unlikely that these worlds are Neptune-like. Image credit: ESA/Hubble.

If we’re looking for life elsewhere in the universe, we have only to consider the range of planetary systems thus far discovered to know that we need to study systems utterly unlike our own. The goal then, as the authors put it, is to measure the total frequency of biology. That makes red dwarfs an obvious target, particularly when, like TRAPPIST-1, nearby examples offer such deep transits, so much more amenable to current study than Earth-sized worlds transiting G-class stars like our Sun. Indeed, a TRAPPIST-1 transit can be 80 times more prominent, with like gains in the visibility of atmospheric chemistry.

So while we continue to search for a true Earth analog around a star like the Sun, we can put nearby red dwarf planets under immediate investigation, with TRAPPIST-1 transits happening in a matter of days or weeks rather than once a year. The nature of their atmospheres is the first priority, helping us decide what surface conditions may be like. The search for biosignatures of biologically produced gases follows, with the added advantage at TRAPPIST-1 in having so many planets that can be directly compared to each other.

The TRAPPIST (Transiting Planets and Planetesimals Small Telescopes) facility we used to find the TRAPPIST-1 planets was just the prototype of a more ambitious planet survey called SPECULOOS (Search for habitable Planets Eclipsing Ultra-Cool Stars), which has already begun operations. We expect to find many more Earth-sized, rocky planets around dwarf stars within the next five years. With this sample in hand, we will explore the many climates of such worlds. The solar system contains two: Venus and Earth. How many different types of environments will we discover?

If red dwarf planets near us are shown to be devoid of life, we may eventually learn that life is rarer than we thought. But I return to my earlier sentiment — at heart, our goal in studying the universe isn’t to find life, but rather to find what is out there. If we were to learn that life is vanishingly rare, that would be a finding of immense significance for our stewardship of our own planet, teaching us how unusual it may in fact be. In any case, while we all have ideas about what we hope to find, the universe will surely keep forcing us to adjust our expectations.

“Certainly the search for life elsewhere compels us to find planets like our own around stars much like the Sun”.

Please don’t talk for all of us. I never liked and never agreed with the mainstream dogma that equates habitability to liquid water on the surface or other Earth-like conditions. I’m happy that the research community is sloooowly, very slowly, moving away from that prejudice, as the two recent posts show. But still there is a long way to go.

Indeed–this is an “Earth chauvinism,” as Carl Sagan would say. :-) It is better to think of Earth life, humanity, and terrestrial technological civilization as one set of *models* which, having occurred here, could also occur elsewhere, upon similar worlds. But being the only such models we know, it is intellectually self-impoverishing to assume that they are the ^only^ viable, workable models for life, intelligence, and civilization that can exist. The only problem–but a simultaneously frustrating and delightful one–that these unknown other possible models present is that we can’t know exactly what to look for (including the abodes of such beings–what are livable homes, on planets or even elsewhere?).

How would a red dwarf flare star remove large quantities of water from a planet in its hab zone? Also, I’ve read about red dwarf flares for a long time, but I’ve never heard much about the energies involved. Can you provide some idea of what these flares are like? It would be interesting to know how they might be perceived on the surface of a hab zone planet. I envision wild aurorae over the dark side during a flare, but might there also be a blast/steam wave from the light side?

David, probably the best thing for me to do here is quote from Rory Barnes, co-author of the paper that is cited so frequently on this matter. Here’s how he described the situation in a news release:

“Planets around these stars can form within 10 million years, so they are around when the stars are still extremely bright. And that’s not good for habitability, since these planets are going to initially be very hot, with surface temperatures in excess of a thousand degrees. When this happens, your oceans boil and your entire atmosphere becomes steam.”

Then throw in the fact of M dwarf flares with lots of X-ray and ultraviolet light. This heats the upper atmosphere to thousands of degrees, according to Barnes and Luger, and causes gas to expand so quickly it leaves the planet and is lost to space. What had been oceans go dry.

Check the paper: “Extreme Water Loss and Abiotic O2 Buildup On Planets Throughout the Habitable Zones of M Dwarfs,” available here:

“The stellar activity of M dwarfs is high, resulting in large amounts of XUV radiation emitted toward the surface of the planet, which may cause atmospheric erosion (Lammer et al., 2007), a runaway greenhouse, and hydrodynamic escape on close orbiting planets (Luger & Barnes, 2015). Over the ∼1 Gyr of an M-dwarf star’s intense activity, a planet orbiting in its habitable zone could have been bombarded with this XUV radiation. By the time the M dwarf has settled onto the Main Sequence, planets that were once habitable may have lost oceans worth of water to space, and could be long dessicated and void of surface life (Luger & Barnes, 2015). However, a recent study of possible water loss in the atmospheres of ultracool dwarfs (Teff < ∼ 3000 K) found that the TRAPPIST-1 planets (Gillon et al., 2016), particularly TRAPPIST-1d, may still have retained enough water to maintain surface habitability, depending on their original water inventories (Bolmont et al., 2016b).”
So the jury is still out on how likely ocean survival is.
On the matter of what a flare would be like from the surface of a red dwarf planet, I think you’re right about the auroral effect but haven’t seen much about related phenomena. An interesting question, and worth exploring in terms of science fiction settings among much else! Maybe one of the readers has a reference or two on this.

What is it we are looking for when we probe nearby planetary systems? Well, the human-oriented answer to that, the answer that you may not want to hear, is: we will be looking for desirable real estate that (when we develop transport) we can expand our presence to, colonize, and fill up. Rather as in ‘The Big Hunger’ by Walter M. Miller.

From this point of view, sapient inhabitants capable of putting up determined resistance, or worse, capable of winning, would be a decidedly disadvantageous feature of a planet. It might well be the case that the ideal planet would be one that had no indigenous life at all, if we find (and this is not a given) that independently arising extraterrestrial life is generally chemically and biologically incompatible with us and with the plants and animals that we will want to propagate for feeding us. The job of decontaminating a planet that has already developed independent life may be very difficult, and may be biologically impossible. So a tabula rasa, ready for simple terraforming, may be the best bet.

Honestly, I highly doubt that when we finally become able to travel to Alpha Centauri, we haven’t colonized the entire Solar System and thus can live confortably in celestial bodies very different from the Earth.

Thus, even defining ‘habitable zone’ as ‘zone that men can inhabit’, it will not be equivalent to ‘liquid water in the surface’.

Good comment…
We have Mars through which we will discover many things…
The robots of today might not be so dumb in a hundred years…
Self learning humanoid artilects could go to the Centauri system…
Project Longshot would get there in just one century…
The artilect needn’t make the return trip–ever…
It’s our permanent outpost in the Centauri system…

”…So a tabula rasa, ready for simple terraforming, may be the best bet.” Perhaps thats true , but it might take several millions of years to terrraform a planet similar to earth before the event of Life .
When life first started to produce oxygen , gigantic quantities of O2 was consumed by chemical processes , and only when these were completely saturated , did free O2 start to build up ….so it might NOT be an early earth we are loking for . …but there might exist other scenaria which could shortcut the unpleasant million-year-problem :
One possibillity is to look for a relativly YOUNG planet with an existing biology and the beginning of an O2 atmosphere , and try to establish earthlife on an Island small enough to be completely sterilized for a limited period , long enough to give eartlife a fighting chance….all we know about evolution leads us to the conclution that TIME is an important factor , and that ”older” , more ”experienced ‘ life forms usually will out-compete the ”younger ones —so earth’s more mature lifevariationes having fougt themselves for 2billion years MORE than the locals ,might have a serious advantage over the locals , given a protected start .
Another ,and perhaps more generally aceptable, way to speed up terraforming , is to look for a planet which has no Life , but an oxygen atmosphere produced by the selective loss of H2, blown away by the solar wind …..in this case a planet with very deep oceans comes to mind …a ”Waterworld” …..but too much O2 could become a serious problem later , when photosyntesis became dominant

The way to answer unknowns is to limit the question through the most physical scientific principles as one can which includes Occam’s Razor. There may be contingencies for life to exist long term which might all need to be satisfied. With tidally locked planets these contingencies might all add up to make it too difficult for life. Too much ultra violet radiation might make sterile planets. The atmospheric loss from the solar wind by a lack of a magnetic field will make an atmosphere thin which is what one does not want since x rays will be blocked by a thick atmosphere like Earth’s. It does not necessarily mean the all ozone will be removed but some oxygen will be lost over time which is needed to create ozone. The depletion rate should be less than the oxygen production rate by life.

Life could evolve if enough oxygen is produced. The question is will it be able to be maintained for a long time which is an unknown. Only the accurate spectra of the planet will be able to rule life out. If there is no oxygen, ozone or methane or nitrogen it will have to be ruled out. We will have to wait for the James Webb Space telescope and other large ground based ones to become operational. The solar wind can remove a lot of hydrogen and therefore water from an atmosphere over a geologic time scale.

A tidally locked planet most likely does not have a magnetic field since it takes the circling or convection motion of charged particles to make a magnetic field. All the planets in our solar system, the gas giants and Earth have a magnetosphere and powerful magnetic field due to a fast rotation which causes the Coriolis deflection of convection currents of pressure ionized charged particles in liquid metallic hydrogen or an circling motion in a liquid iron core as in Earth’s core. Without that fast rotation, there will be no magnetic field such as seen in Venus. Mars is too small to keep a liquid iron core which became solid or it’s rotation is too slow for it’s size.

Just not to be over pessimistic. Stellar wind takes much longer timescale to erode an atmosphere. The oxygen ion escape calculated on Proxima b and TRAPPIST-1 system 10^27/s is only 2 orders of magnitude higher than Earth, and on Earth CO2 particle outgassing rate from volcanic and tectonic activities is 10^29/s, so it would be fine as long as the plate tectonics operate on the planet, because the escaping atmosphere can be replenished by outgassing gases (Dong et al., 2017; Dong et al., 2018; Catling & Kasting, 2017).
Another study assumed Earth-like geophysical properties and atmosphere and found the *max* escape rate of H+ and O+ is 10^6g/s, but on Earth, H2O outgassing rate is above 10^7g/s (Garcia-Sage et al., 2017; Catling & Kasting, 2017). Therefore, it is totally possible to maintain atmospheres around M-dwarfs.

Slow rotation (tidal locking) might have negative impact on the strength of the magnetic field, but planets are possible to have magnetosphere large enough to keep exobase in protection under average stellar wind (which does not include CMEs; Zuluaga et al., 2013; Vidotto et al., 2013). Additionally, ionosphere induced magnetic field should also play a role in shielding the planets that lack intrinsic magnetic field, like Venus or Earth during geomagnetic reversal (Birk et al., 2004).

Very interesting. I didn’t know that M dwarf exoplanets can loose an oceans worth of water and a lot of atmosphere early due to XUV radiation during the early extremely bright period. Maybe the inverse square law plays a role since M dwarf explanets are much closer. That effect will be somewhat reduced if they migrated but they would have to migrate a long way.

That study has some caveats. First, they assumed that during PSM, all the water is on the planet surface. This might work in magma ocean scenario, but in a solid exoplanet, a large quantity of water can be stored in mantle and released back in later time. Second, planets are expected to be born with thin hydrogen envelope, which can protect the planets from being dessicated(Owen & Mohanty, 2016)

We need to look for things we can USE…planets, dust, rocks, energy…
Life is important and we shouldn’t interfere with any life we find, but I doubt that will be a serious limitation. There’s apparently plenty of stuff for everybody.

This seems to be a neglected class and they may have over three times as many stars as Sol – G type dwarfs. Hopefully TESS will bring us up to speed on the numbers of these local transiting K dwarfs, but what of any earth based observations? What would be nice is to see the relationship between M, K, G, and F type stars that have transiting planets from Kepler and ground based observations, this could tell us a lot about how these different dwarf star develop planets.

From SolStation.com

Roughly a thousand stars (947+) of spectral type “K” have been tentatively identified and located within 100 light-years (ly) or (or 30.7 parsecs) of Sol, but only 155 within 50 ly.

In the case of these relatively dim and difficult to study stars, we should examine first the inner sphere of space within 50 ly of Sol. Only around 26 are now known to be located within 25 ly, while another 127 are estimated to lie between 25 and 50 light-years. However, based on the known density of K stars within 25 ly, we would expect a total of 216-some stars within 50 ly, rather than only 155. A comparison of the density of K-type stars between the two volumes of space indicates that the outer spherical shell has around two-thirds (68 percent) of the spatial density of known K-type stars as the inner spherical volume, which suggests that astronomers have yet to identify a significant share of K-type stars that are actually located within 50 ly of Sol — much less within 100 ly.

If we anticipate that around 216 K-type stars may eventually be found within 50 light-years (ly) of Sol, then we would expect that around 1,728 stars may eventually be found within 100 ly. However, since only around 949 some K-type stars are known to be located within the 100-ly sphere, it may be that astronomers have only identified around 55 percent of these relatively dim stars that are actually located within 100 ly of Sol. Indeed, many K-type stars that are already cataloged lack high-precision parallax estimates, and others may be mis-typed as early M-type stars. As relatively common binary companions of brighter stars, some K stars may be orbiting too close to have been spectrally typed with high confidence.

I agree. Forget the M’s. The K’s are where its at. They are more numerous, don’t flare like the M’s, and have longer lifespan than the G’s. One benefit of K’s is their habitable zone planets are not tidally locked like those of the M’s.

It all depends on WHAT TYPE OF LIFE you expect to find! If you expect extremophiles forming on these planets, you’re in luck. There’s gazillions of them out there! This is great, because this will be great PRACTICE for astronomers to refine their techniques. Discovering strong evidence for extremophilic life, AND; characterizing the atmosphere’s of these planets IN GREAT DETAIL, means that finding evidence of MORE COMPLEX LIFE on planets orbiting Sun-like planets will be giver greater credence. Photosynthesis: Not so much. As of now, we don’t even know if organisms can evolve an efficient enough photosynthetic system to use the meager OPTICAL light these stars provide. And as for multi-cellular(and eventually intelligent technological)life, forget about it! Here’s my reasoning on this one: There appear to be MANY ORDERS OF MAGNITUDE rocky planets with moderate temperatures around M dwarfs than K,G, and F dwarfs COMBINED! Take the worst-case scenario that we are the only CURRENT technological society from a G dwarf in the entire galaxy. Then we can assume hundreds of such societies on planets like TRAPPIST-1e. That being the case, EXPANSION of these societies over billions of years would mean that ONE of these societies would be HERE right now! Obviously that is not the case. However, we should still try to messages and technosignatures from these stars, because that would mean that they have been SUCCESSFULLY COLONIZED by ETI’s that ORIGINATED on Sun-like stars, and that, this being POSSIBLE, OUR dreams of colonizing Proxima b are achievable, superflares bedamned!

It is entirely possible that the most common biosphere is under the ice such as proposed for Europa.

Good luck for detecting that across interstellar space unless . . . intelligent life develops, breaches the icy confines and reaches out to other ice worlds. Obviously, life developing on the surface of other planets would be considered highly improbable by our icy fellow-travelers due to extremes of radiation from solar flares, eroded atmosphere and wildly variable climate. Even if intelligent life were to develop, any surface inhabitants of such a world would be driven mad upon realization that a thin layer of gas is all that stands between them and eternity. Surface life can never evolve beyond the hardy microbe level under the most optimistic scenario!

I concur with those who think we should be open to investigating all sorts of phenomena, even when seeking life. Earth life may be just one model, and I mean this in the widest possible sense, not just details of cell-based, replicators with metabolisms. Life as we don’t know it might even be difficult to recognize as life. Obviously, we will look for life based on terrestrial forms, but we should be open to expanding our views on “What is Life?” (c.f. Schrödinger, 1944) when we explore worlds with our probes. Even within our own system, it is just possible that we may discover phenomena that could be described as life, or “pre-life” but bear little resemblance to terrestrial organisms.

Nicky this paper claims the opposite. https://www.aanda.org/articles/aa/full_html/2013/09/aa21504-13/aa21504-13.html The magnetic field of the M Class dwarf will weaken the magnetic field of the exoplanet so that solar wind stripping still occurs. Also I am biased against the idea that there can be a planet with a slow rotation and a magnetic field strong enough to block solar wind. There are no examples of such planets in our solar system, but that does not mean they don’t exist elsewhere. Scientists stick to general principles until they are contradicted and so do I.

Geoffrey Hillend, that paper does not. It rather suggests that maintaining Earth-like magnetosphere (extending up to 60,000 km) is hard in M-dwarf habitable zone, but keeping exobase (below it is thermosphere where ionization takes place; depending on composition, CO2 is resistant to thermal expansion, but Earth-like is not) under protection is totally possible (that is what I said earlier). Vidotte is not a geophysicist, his main focus is planet-wind interaction. Zuluaga is the scientist that studies the origin of magnetic field doi.org/10.1088/0004-637X/770/1/23
This paper (arxiv.org/abs/1608.06919) about Proxima b also predicts it can have magnetic moment as strong as Earth.
As I have already pointed out, studies of ion escape (including stellar wind pick-up, charge exchange, etc.) on unmagnetized planets show that it can be replenished by Earth-like volcanic activity.

If advanced intelligent life could develop over short time periods on planets around A ans F type stars this could change Drake’s equation. The reason being that over the 12 billion years our galaxy has existed those two groups would have made up a total population of 16 percent of all stars. Stars from G to M are still in their first generation but the number we now see as F and A type stars have gone thru from 4 to possible as high as 40 generations for early type A stars. These stars also do not flare and have much wider habitable zones with many more planets in that zone!

But how long did it take large brain life to develop here? If you look at Earth as not the perfect place for life to develop, then a perfect planet and star may jump from early micro life to something like the Cambrian explosion very quickly. When did large brains appear, after the dinosaurs were wiped out, so could evolution also jump from fish to something like mammals directly? What were the first large brain mammals, Elephants, whales, dolphins or some other species that disappeared or never made it past the size of a cat’s brain? The 500 million years that is stable in A class stars may be enough time and there has been many more A class stars over the life of our galaxy. So these civilizations that could have developed on the planets around A class stars would have to of developed interstellar travel or some other method to circumnavigate their imminent doom of their star.

Do A-type stars flare?
(Submitted on 14 Dec 2016)

“For flares to be generated, stars have to have a sufficiently deep outer convection zone (F5 and later), strong large–scale magnetic fields (Ap/Bp-type stars) or strong, radiatively driven winds (B5 and earlier). Normal A-type stars possess none of these and therefore should not flare. Nevertheless, flares have previously been detected in the Kepler lightcurves of 33 A-type stars and interpreted to be intrinsic to the stars. Here we present new and detailed analyses of these 33 stars, imposing very strict criteria for the flare detection. We confirm the presence of flare-like features in 27 of the 33 A-type stars. A study of the pixel data and the surrounding field-of-view (FOV) reveals that 14 of these 27 flaring objects have overlapping neighbouring stars and 5 stars show clear contamination in the pixel data. We have obtained high-resolution spectra for 2/3 of the entire sample and confirm that our targets are indeed A-type stars. Detailed analyses revealed that 11 out of 19 stars with multiple epochs of observations are spectroscopic binaries. Furthermore, and contrary to previous studies, we find that the flares can originate from a cooler, unresolved companion. We note the presence of Hα emission in eight stars. Whether this emission is circumstellar or magnetic in origin is unknown. In summary, we find possible alternative explanations for the observed flares for at least 19 of the 33 A-type stars, but find no truly convincing target to support the hypothesis of flaring A-type stars.”

While the researchers acknowledge that UV can be damaging to RNA, they discovered that some parts of the molecule act as a protective shield for other parts. The nitrogenous bases absorb and disperse UV radiation, protecting the RNA’s pentose-phosphate backbone
“Apparently, the backbones of DNA and RNA can be rescued by the partial “victimization” of the nitrogenous bases,” the scientists write. “One can assume that these bases had been selected to perform the UV-protecting function before they became involved in the maintenance and transfer of genetic information.”
Since double strands provide more UV protection to the RNA backbone than single-strands, the scientists suggest that base-pairing may have originated as a trait to provide greater UV protection. Only later did these bases evolve to perform their current functions.
In the computer simulation, the stability of RNA under UV radiation gave the molecules a selective advantage, allowing the number of RNA molecules to increase under natural selection.

So what they are saying is that an ozone layer must develop for advance life to evolve. A and F type stars emit large amounts of UV and this could split H2O to form the protective layer. Around A types, the Jupiter size planets are three times more common than G types. Earth size moons could with substantial oceans have evolved advanced life and tidally locked, may have land masses facing the main planet.

Another problem with A and F stars is being able to find planets around them. They tend to swamp the signal for transits, the astrometric is difficult because of the ratio mass of star to planet and radial velocity is not accurate because of line broadening do to fast rotation. There is one way we may be able to detect smaller planets, according to Shklovskii and Sagan 22 percent of A type stars and 30 percent of F0 thru F2 have rotational velocities o to 50 km per sec-1, this is the same as G,K,M stars. There are ways to filter out the photospheric activity, so we need to start looking for smaller planets around such stars with the new instruments coming online. They also say that Ao stars last 400 million years on the main sequence, I have noticed a lot of discrepancy in stars lifetimes as they grow in mass, this may be related to metal abundances. As Paul says; “We ignore preconceptions to find out which is true.”

From the point of view of pure science, we would have little to gain by discovering a planet exactly like ours, orbiting a star exactly like ours, with life exactly like ours, compared to discoveries that force us to rethink our definitions of life and of intelligence.
Obviously, our vast universe will offer abundant examples of each.

Quote by Nicky: “As I have already pointed out, studies of ion escape (including stellar wind pick-up, charge exchange, etc.) on unmagnetized planets show that it can be replenished by Earth-like volcanic activity.” Venus is a good example. It also has a slow rotation and no magnetic field.

Well, Venus’s CO2 atmosphere is clearly still there. The lack of water is mainly due to hydrodynamic escape (thermal escape) not ion escape (nonthermal escape) induced by solar wind, which has nothing to do with magnetic field. Because thermal escape rate does not depend on magnetic protection, but ion does. Under Venus-level insolation, regardless how strong the field is, water would still be lost. Venus CO2 atmosphere is not blew away, which contains almost the same amount of carbon as Earth does. Venus is an example that opposes your point.
The correlation of nonmagnetic feature and slow rotation of Venus seems tempting, but that is not the main cause. The shut down of dynamo cannot be only explained by slow rotation, it involves the evolutionary path of the planet. Mercury’s dynamo is still working even being tidal locked. It’s just much weaker than Earth. Lastly, Venus has its own ionosphere induced magnetic field.

Quote by Antonio: “Very interesting hypothesis, that of most ETI originating from A-type stars.” A type stars only have a main sequence life of one billion years. It took 4.5 billion years for life to evolve on Earth which is why astrophysicists and astronomers don’t consider A type stars for ETI origin. Even F type stars have a main sequence lifetime of only five billion years which means that get too hot for life only halfway through that period so ETI origin there is also improbable.

Yes, but that is addressed in Michael Fidler’s comment. If development of intelligence on Earth is not typical but quite longer than usual, and planets can generate intelligent species in a few hundred million years, then his hypothesis is possible.

Yes, but that is from our point of view, which life has to have a long gestation (3.5 billion years) before it can evolve into multicelluar organisms. This may not be the case on all planets, the norm may be a much shorter time period.
The F and A type stars are not even being looked at as the dogma says they are uninhabitable. The Sept. 4, 2017 article on Science Alert “How Ultraviolet Light Could Point to Alien Life” brings up a good point about M dwarfs not having enough UV radiation and that life may take a long time to develop on the planets around them. So could the A and F stars speed up evolution because of their much higher, steady UV radiation?

Although the UV does increase as the star gets hotter and so could generate more oxygen through photo dissociation potentially accelerating complex life it is offset by a shorter lifespan. But we only need 4.5 billion years to get to where humans have mastered technology in our one sample example so heavier massed stars could produce complex life sooner.

Quote by Antonio: “Nope, you start with a single example (Earth) and assume, out of thin air, that its characteristics define a general principle.”
Do you mean how life evolved? It’s the fossil evidence that proves that human life took billions of years to evolve on Earth which are the principles of scientists I am using. One does not have to use scientific principles and knowledge or even agree with me or scientists. It seems to me the predictions that scientists have made with principles and scientific knowledge have come true about the physical universe. If you want to believe that ETI life can evolve in only 500 million years it’s o.k. with me. I don’t think any real scientists who are specialists in the field will give that view any credibility based on their principles of course. As I have written before they not my principles, but are the ones abstracted or differentiated by scientists from laboratory and empirical research.

“Vega is a slightly bluish, white main sequence dwarf star of spectral and luminosity type A0 V, like Sirius. Although the star was estimated previously to have 2.3 to 3.1 times Sol’s mass, a 2012 analysis now suggests around 2.15 Solar-masses (Ken Croswell, Science Now, December 3, 2012 and Monnier et al, 2012). Vega may also have 2.73 +/- 0.01 times its diameter (Aufdenberg et al, 2006; and Ciardi et al, 2001) and 37 +/- 3 times (true A0V average derived by Aufdenberg et al, 2006) to 58 times (pole on) its luminosity. Like Sirius, however, Vega radiates much more in ultraviolet wavelengths than Sol, and, not surprisingly, the European Space Agency has used ultraviolet spectral flux distribution data to determine stellar effective temperatures and surface gravities, including those of Vega. The star may be about only 63 percent as enriched as Sol with elements heavier than hydrogen (“metallicity”) based on its abundance of iron (D. Gigas, 1986, but more recent findings on Vega’s mild underabundance of metals can be found in Ilijic et al, 1998). On the other hand, its iron metallicity has been measured anywhere from four to 115 percent of Sol’s (Cayrel de Strobel et al, 1991, page 31).

Previously estimated to be only around 200 to 350 million years old (Maeder and Meynet, 1988), more recent estimates of its mass indicate an age of around 625 to 850 million years (Ken Croswell, Science Now, December 3, 2012 and Monnier et al, 2012). As Vega is so much bigger and hotter than Sol, however, the star will exhaust its core hydrogen after only another 650 million years or so (for a total life of around a billion years) and turn into a red giant or Cepheid variable before puffing away its outer layers to reveal a remnant core as a white dwarf. The star is a rapidly rotating star whose apparent “pole-on” view from Earth distorts its various stellar characteristics (Aufdenberg et al, 2006; and Gulliver et al, 1994).”

The lifetime for the hydrogen burning time for Sirius an A1 V is also 1 billion years.

Real Scientist! Really? Most scientist are driven by where the research is most active and the highest number of grants obtainable. A billion years ago all there was on earth were single cell life.

Open-mindedness is receptiveness to new ideas. Open-mindedness relates to the way in which people approach the views and knowledge of others, and “incorporate the beliefs that others should be free to express their views and that the value of others’ knowledge should be recognized.”

Well it is probably better to use the radial velocity for the Kepler canidetes and TESS results. These instruments are having a hard enough time keeping up with Kepler – TESS will be adding more then 20,000 in the first two years! ( Maybe 200,000 in 20 years). TESS will be observing in the red and infrared so it will be good for the M dwarfs, plus it is designed for a 20 year lifetime.

FIRST RADIO EMISSION DETECTED FROM A PLANET ORBITING A STAR OTHER THAN THE SUN!!! “Radio Emission from the Exoplanetary System epsilon Eridani.” by T. S. Bastian, J. Villadsen, A. Maps, G Halinan, A. J. Beasley. “…The location of the 2-4GHz radio pulse is $> 2.5\sigma from the star…” BOTTOM LINE: Either the REPORTED orbit for epsilon Eridani is incorrect, or the signal is coming from ANOTHER planet!!!

As part of a wider search for radio emission from nearby systems known or suspected to contain extrasolar planets ϵ Eridani was observed by the Jansky Very Large Array (VLA) in the 2-4 GHz and 4-8 GHz frequency bands. In addition, as part of a separate survey of thermal emission from solar-like stars, ϵ Eri was observed in the 8-12 GHz and the 12-18 GHz bands of the VLA. Quasi-steady continuum radio emission from ϵ Eri was detected in the three high-frequency bands at levels ranging from 67-83 μ Jy. No significant variability is seen in the quasi-steady emission. The emission in the 2-4 GHz emission, however, is shown to be the result of a circularly polarized (up to 50\%) radio pulse or flare of a few minutes duration that occurred at the beginning of the observation.

We consider the astrometric position of the radio source in each frequency band relative to the expected position of the K2V star and the purported planet. The quasi-steady radio emission at frequencies ≥8 GHz is consistent with a stellar origin. The quality of the 4-8 GHz astrometry provides no meaningful constraint on the origin of the emission. The location of the 2-4 GHz radio pulse is >2.5σ from the star yet, based on the ephemeris of Benedict et al. (2006), it is not consistent with the expected location of the planet either.

If the radio pulse has a planetary origin, then either the planetary ephemeris is incorrect or the emission originates from another planet.

The REASON I assumed it was AU and not milliarcseconds is that the latter would put the planet close to 100 AU from the star, and therefore the authors would not have mentioned the “wrong ephemeris for the reported planet based on radial velocity measurements, because it is impossible to have conclusive evidence for a planet at that distance with just a few decades worth of RV observations. ALSO: The ONLY way I can see a radio pulse being produced by a planet is HIGHLY MAGNETIZED smoke-like dust striking a VERY STRONG planetary magnetic field at a VERY HIGH VELOCITY, again adding credence to the 2.5 AU interpretation over the 2.5 milliarcsecond interpretation.

Nature is very good at making fools of us.
Exoskeletons was a very early evolutionary trait and crabs would be very happy on planets with high UV. So there are many things on Earth that could survive in the hostile enviorments of F and A stars that would burn our Lilly white a–.

Life could certainly evolve on A and F stars. The problem with A stars is that it can’t hang around very long since they become more luminous and hotter as they move of the main sequence of hydrogen burning and begin helium burning much earlier than G, K, and M class stars. The reason being is that the larger the star the faster the burning or hydrogen fuel is needed for radiation to balance the larger gravity and mass of the star in order for there to be a stable star and have a balance between radiation and gravity. Consequently, the shorter the lifetime of the star the more massive it is.

The result is that the life belt around A stars doesn’t remain at the same distance for long. If moves away from the star leaving the original life belt to lot for life. Any Earth like planet there would become like Venus.

The sun was only giving 70% of the light billions of years ago, things always change, they have to for life to form and evolve, if not all you would have is micrometeorites chipping rocks like on the moon. All I am trying to say is that there is the possibility that life could develop on the planets in the F and A class stars, plenty of energy. It is a was not too long ago that M dwarfs where considered non habitual also. Someday we may find out!!!

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last eleven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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